Device for optical monitoring of constituent in tissue or body fluid sample using wavelength modulation spectroscopy, such as for blood glucose levels

Abstract

A device for monitoring the concentration level of a constituent in tissue or a body fluid sample, such as glucose concentration in blood, has a laser light source which is modulated about a center emission frequency to probe the absorption spectrum of the constituent being monitored, a laser driver circuit for tuning and modulating the laser light, a photodetector for detecting light from the laser light source transmitted through the sample as the modulation frequency of the laser is tuned, and a demodulator for demodulating the transmitted light and detecting variations in magnitude at harmonics of the modulation frequency to assess the concentration level of that constituent. The device utilizes short-wavelength near-infrared laser light to monitor blood glucose levels, and could also be used for drug screening and diagnosis of other medical conditions as well. In one embodiment, the device is used to monitor blood glucose level externally from the body and non-invasively by trans-illumination through a thin layer of skin, without the need for physical penetration of the skin. In another embodiment, the device is used as an intravenous sensor deployed through a catheter, and its output can be used to control an insulin pump to stabilize the patient's blood glucose levels.

Description

[0001]This U.S. patent application claims the priority of U.S. Provisional Application No. 60 / 538,988 filed on Jan. 23, 2004, entitled “Non-Invasive Biomedical Sensor”, and U.S. Provisional Application No. 60 / 632,300, filed on Nov. 30, 2004, entitled “Continuous Intravenous Optical Glucose Monitor with Feedback Control for Insulin Pump”, of the same inventors.[0002]The subject matter herein was developed in part under a research grant provided by the U.S. Government, National Science Foundations, Grant / Project No. ECS01-34640, ORS No. R-2001906. The U.S. Government retains certain rights in the invention.TECHNICAL FIELD[0003]This invention generally relates to a device for optical monitoring of a constituent in tissue or body fluid sample, particularly for non-invasive or intravenous blood glucose monitoring.BACKGROUND OF INVENTION[0004]According to the American Diabetes Association, over 6% of the US population is affected by diabetes. Worldwide, the number of people with diabetes ...

AI Technical Summary

Benefits of technology

[0011]In accordance with the present invention, the issues plaguing conventional non-invasive biomedical sensors are overcome by a device which can monitor a constituent in an aqueous sample by employing wavelength-modulation absorption spectroscopy of a laser light probe, and active signal processing and filtering to spectrally stabilize the laser probe, increase the signal-to-noise ratio, and decrease the calculations required.

[0018]The key advantages of this technique are that it exploits the noise reduction associated with coherent detection, allows for referencing and spectral stabilization, and enhances the spectral signature derived by harmonic detection. Furthermore, this measurement technique is conveniently implemented with semiconductor lasers, allowing the device to be constructed for a fraction of the cost of competitive optical systems. Many available laser diode geometries, including edge-emitting lasers and vertical-cavity surface emitting lasers (VCSELs), can be tuned and modulated (both amplitude and wavelength) via injection current. Both heterojunction edge-emitting lasers and VCSELs can be employed for non-invasive sensing.

[0019]In a particular embodiment, the monitoring device is used to monitor blood glucose concentrations externally from the body and non-invasively by transillumination of the photodiode through a thin layer of skin, such as the earlobe or finger webbing, upon which a portion of the light is transmitted through the skin. The transmitted light is detected by a photodetector, spectrally analyzed, and processed by a microprocessor to measure quantitatively and accurately the patient's blood glucose concentration, without the need for physical penetration of the skin. This device can be made portable and conveniently used at home or at any location by people who suffer from diabetes to continuously or periodically monitor blood glucose levels while avoiding the need for finger lancing as is done conventionally. The device can similarly be used to monitor other blood constituents, such as carbon dioxide, hemoglobin, potassium, etc.

Problems solved by technology

Commercially available methods of monitoring glucose levels are invasive and prone to error.

The pain and risk of infection from invasive probes can often deter them from maintaining their prescribed monitoring schedule, escalating the risks of secondary aliments of diabetes mellitus.

However, such prior art devices have limitations that prevent their widespread use, e.g., lack of sensitivity and specificity, interference with other blood constituents and noise limitations.

Conventional noninvasive sensor systems for blood glucose monitoring still require frequent “finger-stick” blood glucose measurements for recalibration purposes, thus defeating its purpose to replace invasive methods.

However, this system is lacking in spectral referencing to completely eliminate spectral drifting of the optical system, and in the proper rationing of higher order derivative features to provide absolute glucose concentrations in varying portions of tissues.

One of the largest obstacles in non-invasive biomedical sensing is variability in the samples from person to person and from day to day.

Numerous variables must be analyzed simultaneously, requiring long and complex multivariate calculations to provide precise measurements of constituents.

The primary limitation of the multivariate analysis used in conventional measurement techniques is that if one of the components is estimated incorrectly, then the whole analysis can be skewed.

This inherent problem can be difficult to isolate and correct in real-time.

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